This invention relates to the preparation of copolymers of ethylene and chlorotrifluoroethylene; more particularly this invention relates to the copolymerization of ethylene and chlorotrifluoroethylene in an aqueous emulsion.
Copolymers of ethylene and chlorotrifluoroethylene have been polymerized using free radical initiation. The free radical initiators include a wide variety of peroxide and oxidation-reduction systems. The oxidation-reduction system is generally in an aqueous suspending medium.
The copolymerization is usually carried out in an aqueous suspension of chlorotrifluoroethylene with ethylene dissolved in it or in a bulk state of chlorotrifluoroethylene in contact with gaseous ethylene. The polymer composition can be adjusted by either the ethylene pressure or the reaction temperature. The physical or mechanical properties of the copolymers formed depend not only on the polymer composition but also on the degree of alternation of the monomers. The degree of alternation of the monomers is determined largely by the reaction temperature. The pH of the aqueous medium can affect the rate of polymerization. The pH of the aqueous medium can be controlled by a buffering agent and arranged between 7 and 12, and preferably, between 7 and 9. U.S. Pat. No. 3,767,634 discloses a process of copolymerizing chlorotrifluoroethylene and ethylene using an oxidizing agent and a reducing agent where there is a sufficient amount of a water-soluble buffer compound to maintain the pH above 7 and up to about 12. U.S. Ser. No. 330,120, filed Dec. 14, 1981, hereby incorporated by reference, discloses the use of copper salts in redox polymerization of ethylene chlorotrifluoroethylene.
The method of emulsion polymerization is well known and has been used for various polymers and elastomers. The emulsion polymerized polymers are generally characterized by high polymerization rates, high molecular weight polymers and a product which is an aqueous latex. It is known to emulsion polymerize a variety of fluoropolymers. U.S. Pat. Nos. 3,857,827 and 4,025,709 disclose the emulsion polymerization of polyvinylidine fluoride. U.S. Pat. No. 4,225,482 discloses the emulsion polymerization of the copolymer of tetrafluoroethylene and ethylene. U.S. Pat. Nos. 3,006,881 and 3,043,823 disclose the emulsion polymerization of polychlorotrifluoroethylene.
Aqueous dispersions of ethylene chlorotrifluoroethylene copolymers have been made by dispersing ground copolymer powder using dispersion agents. The present invention relates to the formation of the copolymer of ethylene and chlorotrifluoroethylene by emulsion polymerization resulting in an aqueous latex emulsion.